Devices driven by flexible drive means, such as flexible belts or chains, are well known. In the automotive field, common examples of such devices include accessory devices, such as water pumps, alternators, power steering pumps, air conditioning compressors, etc. driven by a front engine accessory drive (“FEAD”) or rear engine accessory drive (“READ”). Other examples can include belt-driven superchargers for internal combustion engines or a wide range of other devices driven from the internal combustion engine through a flexible drive.
The design and construction of FEAD and other flexible drive systems has been improved in the last several years by the provision of isolators and/or overrunning decouplers, instead of solid pulleys, on various high load/high inertia devices.
An isolator provides a resilient link, often a coil spring, between the flexible drive and the driven accessory device and the provided resiliency can reduce and/or dampen torsional vibration in the flexible drive which can otherwise adversely affect the expected operating lifetime of the flexible drive. In automotive applications, isolators have been employed as the crankshaft pulley and/or as the drive pulleys at various other accessory devices driven by the flexible drive means. Examples of prior art isolators are described in U.S. Pat. Nos. 5,139,463 and 7,153,227.
An overrunning decoupler provides a resilient link between the flexible drive means and the driven device in one direction, typically when the device is being driven by the flexible drive, and also prevents high inertia devices, such as alternators, from driving the flexible drive when the engine decelerates by allowing the device to overrun its drive pulley and the flexible drive. Examples of prior art decouplers are described in WO 2004/011818; WO 98/50709; U.S. Pat. Nos. 5,156,573 and 6,044,943.
While isolators and/or overrunning decouplers improve the operation and longevity of flexible drive systems, more recently automobiles, trucks and other vehicles have begun to employ various hybrid strategies for their drive systems. Such hybrid strategies include combined internal combustion engine/electric drive strategies and/or start/stop strategies.
With vehicles employing start/stop hybrid strategies, once the internal combustion engine has achieved a preselected set of conditions/parameters, such as reaching a selected operating temperature, the internal combustion engine is shut down whenever the vehicle is stopped in traffic or at traffic lights, etc. and is restarted when the vehicle is to be moved again. One common method of restarting the internal combustion engine in a start/stop hybrid is with an alternator-starter device on a flexible drive, such as a FEAD, and this system is typically referred to as a Belt Alternator Starter (“BAS”) system.
When the internal combustion engine is running in a BAS system, the alternator-starter is functioning as an alternator, producing electrical current for the vehicle and/or charging the storage battery of the vehicle. When the internal combustion engine is stopped, the alternator-starter can draw current from the storage battery and can operate as a starter motor, rotating the crankshaft of the engine via the flexible drive, to restart the engine. Further, in some cases BAS systems can provide a boost mode wherein the alternator-starter can draw current from the storage battery of the vehicle when the engine is running to provide additional power to the engine via the torque supplied to the engine from the alternator-starter via the flexible drive. Such a boost mode can be useful in situations such as passing another vehicle or wherever additional power is required for limited periods of time.
While BAS systems can provide many advantages, the very high inertia of the alternator-starter device can affect the operation and longevity of the flexible drive system, yet the necessity for the alternator-starter, when operating as a starter, to transfer high amounts of torque to the engine through the flexible drive means prevents the use of conventional isolators or overrunning decouplers.
It has been proposed to provide a decoupler with an inertia activated locking mechanism as shown in WO 2007/1003052.
It is desired to have an isolator which can be used with BAS systems and other flexible drive devices which require transfer of relatively high levels of torque in one direction between the device and the flexible drive and at least some degree of isolation when transferring torque in the opposite direction.